Reactions of Group 2 Compounds

This lesson covers: 

  1. Solubility trends of group 2 compounds
  2. Thermal stability trends of group 2 carbonates and nitrates
  3. Reactions of group 2 oxides, hydroxides and carbonates

Opposite solubility trends for group 2 hydroxides and sulfates

The solubility of group 2 metal hydroxides and sulfates follows opposite trends down the group:

  • Group 2 metal hydroxides become more soluble down the group
  • Group 2 metal sulfates become less soluble down the group


This is summarised in the table below:

Group 2 elementSolubility of hydroxideSolubility of sulfate
MagnesiumInsolubleSoluble
CalciumSparingly solubleSparingly soluble
StrontiumSolubleInsoluble
BariumSolubleInsoluble

Thermal stability increases down group 2

The carbonates and nitrates of group 2 elements decompose when heated. The thermal stability (i.e. the temperature needed for decomposition) increases down the group.


Group 2 metal carbonates (MCO3) decompose to oxides and carbon dioxide:

  • MCO3(s) ➔ MO(s) + CO2(g)

Using calcium as an example:

  • CaCO3(s) ➔ CaO(s) + CO2(g)


Group 2 metal nitrates, (M(NO3)2) decompose to oxides, nitrogen dioxide and oxygen:

  • 2M(NO3)2(s) ➔ 2MO(s) + 4NO2(g) + O2(g)

Using calcium as an example:

  • 2Ca(NO3)2(s) ➔ 2CaO(s) + 4NO2(g) + O2(g)

Reactions of group 2 oxides, hydroxides and carbonates

The oxides, hydroxides, and carbonates of group 2 elements are basic and alkaline:


Group 2 metal oxides (MO) readily react with water to form metal hydroxides that dissolve in water:

  • MO(s) + H2O(l) ➔ M(OH)2(aq)

This releases hydroxide ions (OH-) making the solutions strongly alkaline. For example:

  • BaO(s) + H2O(l) ➔ Ba2+(aq) + 2OH-(aq)

The pH of the resulting solutions increases down the group as the solubility of the hydroxides increases.

An exception is MgO which reacts slowly and has low solubility.


Group 2 metal hydroxides (M(OH)2) and carbonates (MCO3) also react with dilute acids such as hydrochloric acid (HCl) to form salt and water:

  • M(OH)2(s) + 2HCl(aq) ➔ MCl2(aq) + 2H2O(l)
  • MCO3(s) + 2HCl(aq) ➔ MCl2(aq) + H2O(l) + CO2(g)

The reactions become more vigorous down the group as the solubility of the compounds increases.